Determination and correlation of in vitro viability for hairless mouse and human neonatal whole skin and stratum corneum/epidermis

Background and design: Viable tissue is essential to assess the rate and extent of biotransformation during percutaneous absorption in vitro. We assessed the viability of hairless mouse whole skin (WS) and stratum cornieum/epidermis (SCE) and human neonatal SCE following separation from the dermis by EDTA phosphate-buffered saline (EDTA-PBS) incubation or by heat treatment by measuring the conversion of dextrose to lactate. Lactate concentrations in receptor fluid samples were determined using a Sigma diagnostic lactate determination kit. A standard curve was prepared and samples assayed spectre photometrically at 340 nm using a lambda 2β spectrophotometer. Standard curves were prepared for each experiment and correlation coefficient values (r) were calculated. Results: Our results showed that heirless mouse SCE was associated with glucose conversion to lactic acid at an increased rate if incubated in EDTA-PBS for 4 h and used immediately. Lactate production was greater with the dermis present (EDTA-PBS WS). The rate of glucose to lactate conversion in hairless mouse SCE was 20-25% of that found in WS. Compared with Dulbecco's modified PBS (DMPBS)-treated WS controls, the rate of lactate production in EDTA-PBS-treated WS was nearly a 50% less. Heat treatment in water at 60°C to separate SCE from hairless mouse WS appeared to eliminate viability. Viability of hairless mouse SCE, as measured by glucose conversion to lactate, was comparable to human neonatal SCE. Conclusions. These results suggest that the dermis is a significant contributor to glucose metabolism and that incubation in EDTA-PBS is a contributing factor to the overall decrease in metabolic capacity of the tissue. As a result of these findings, hairless mouse SCE appears to be useful as a model for human neonatal SCE in percutaneous absorption studies.